AnchorsFactory

Rule-driven anchor placement for UFO fonts. You describe, in a compact text file, where anchors should sit on your glyphs; AnchorsFactory computes the coordinates from each glyph's own geometry and writes the anchors into the font.

It does the pre-marking step of accent handling: place top/bottom/_top/… anchors consistently across hundreds of glyphs, so a tool like GlyphConstruction can then assemble composite glyphs by snapping mark anchors to base anchors.

Install

pip install anchorsfactory
# or, from a checkout:
pip install -e .

Requires Python 3.10+, fontParts and fontTools.

Quick start

# place anchors using the bundled default ruleset, save to font_anchored.ufo
anchorsfactory MyFont.ufo --rules default

# your own rules, overwrite in place, with a backup of existing anchors
anchorsfactory MyFont.ufo --rules my-rules.af --in-place --backup-dir backups/

# a whole folder of UFOs
anchorsfactory masters/ --rules default

By default the source UFO is never overwritten — output goes to *_anchored.ufo unless you pass --in-place.

The rule language

Rules are stacked: define reusable labels, then mark glyphs with them, mixing labels and one-off anchors. An anchor is a name and a parenthesised X Y placement.

# a label
@ = top (box.center capHeight), bottom (box.center 0)

# apply it, by name / unicode / range
A = @, ogonek (outline.right 0)
U+0410..U+044F = @            # all Russian Cyrillic
U+0413 += desc (outline.right 0)   # Г also gets a descender anchor

• X is frame.position: width.* (advance), box.* (bounding box) or outline.* (the contour at height Y, with .first/.last to pick a stem).
• Y is a number, a font metric (capHeight, xHeight, ascender, …), or a reference glyph ($H, $H.bottom, $H*5/6).
• Selectors: name, U+XXXX, range U+A..U+B, glob *.sc, category {Lu}.
• = replace · += add · -= remove; !extends default inherits a ruleset.

Full reference: docs/anchor-rules.md.

Presets and migration

Bundled rulesets default and default-italics are usable by name in --rules or !extends. Old .txt rule files (see examples/) convert to the new syntax — verified lossless:

anchorsfactory-convert examples/default-anchors-list.txt -o my-rules.af

Library API

from anchorsfactory import process_ufo, load_document, apply_document

process_ufo("MyFont.ufo", "default")          # high-level: open, apply, save

from fontParts.world import OpenFont
font = OpenFont("MyFont.ufo")
apply_document(font, load_document("my-rules.af"))
font.save()

Compute without mutating (preview)

compute_document is the functional core: it returns the anchors a rule document would place, keyed by glyph, without touching the font. It owns the same orchestration as apply_document (suffix expansion, shift_x, rounding, same-name dedup), so a preview never drifts from what gets written.

from anchorsfactory import compute_document, load_document, accumulate, resolve

doc = load_document("default")
placed = compute_document(font, doc)          # {glyph_name: [(anchor, x, y), ...]}

# resolve() is the pure, single-anchor primitive behind it:
specs = accumulate(doc, "A", font["A"].unicodes)   # the anchors due on glyph A
x, y = resolve(font, font["A"], specs[0])

For an interactive editor, on_error="collect" never raises — it places what it can and reports the rest as structured diagnostics:

result = compute_document(font, doc, on_error="collect")
for d in result.diagnostics:
    # d.severity == "error"   -> anchor skipped (geometry raised)
    # d.severity == "warning" -> anchor placed via a fallback, but suspect
    print(d.severity, d.glyph, d.anchor, d.reason)

result is a plain dict subclass (so it works anywhere a dict does) carrying a .diagnostics list of ComputeDiagnostic(glyph, anchor, reason, severity, rule). The default on_error="raise" is unchanged and keeps .diagnostics empty.

Development

make venv      # create .venv, install the package (editable) + dev deps, via uv
make test      # run the test suite
make build     # build sdist + wheel into dist/
make release   # bump minor, update CHANGELOG, build, upload to PyPI, tag + push

Releases are cut with make release: it bumps the minor version, fills in a CHANGELOG section from the commit log, publishes to PyPI, and tags vX.Y.Z. Set UV_PUBLISH_TOKEN first; use make release-test to rehearse against TestPyPI.

License

MIT — see LICENSE.